Things to Know (#)





#Prokaryote vs Eukaryote



#Endosymbiosis



#Eukaryote Reproduction



#A.O.G.

Van Leeuwenoek: First Microbiologist






“For me this was among all the marvels that I have discovered in nature the most marvelous of all, and I must say that, for my part, no more pleasant sight has yet met my eye than this of so many thousands of living creatures in one small drop of water, all huddling and moving, but each creature having its own motion.”

Protists: The big picture


  • All Eukaryotes are protists except plants, animals and fungi
    • mostly unicellular
    • several ‘supergroups’


  • Extraordinarily diverse
    • 60,000 species described

    • autotrophs, heterotrophs, or mixotrophs
    • asexual or sexual reproduction
    • functions carried out by organelles
    • membrane bound nucleus


  • First undisputed fossils ~1.8 bya
    • spherical algal protists
    • many protists do not make fossils
    • common ancestry unresolved

First protist fossils, Reticella corrugata - 1.8bya


Basic protist cell: Euglena


Single-celled does not = simple for Eukaryotes. Protists can have very elaborate cells

How did Eukaryotic cells evolve?


  • Origin of the nuclear membrane?


  • Origin of mitochondria (organelle that produces energy)?
    • All eukaryotic cells have mitochondria
    • so mitochondria are homologous…


  • Origin of chloroplasts?
    • Photosynthetic eukaryotes have chloroplasts
    • some from common ancestor
    • others….?


How did Eukaryotic cells evolve?


  • Origin of the nuclear membrane?


  • Origin of mitochondria (organelle that produces energy)?
    • All eukaryotic cells have mitochondria
    • so mitochondria are homologous…


  • Origin of chloroplasts?
    • Photosynthetic eukaryotes have chloroplasts
    • some from common ancestor
    • others….?


  • Endosymbiosis: Organisms of one species living inside an organism of another species
    • undigested prey? internal parasites?

Origin of the nucleus (several theories exist)


We do not know whether nucleus or organelles occurred first!

Origin of the nuclear envelope/membrane


Does data support Endosymbiosis Theory? YES!!!


  • Mitochondria and chloroplasts are about the size of an average bacterium


  • Both organelles replicate independently by fission, as do bacteria
    • have their own ribosomes to make their own proteins
    • mitochondria/chloroplasts each have a circular chromosome


  • Both organelles have double membranes consistent with the engulfing mechanism


  • Genes of each organelle closely resemble ancestors!
    • cyanobacteria for chloroplasts
    • proteobacteria for mitrochondria
    • some genes have shifted from bacteria to host, possibly explaining why ‘mitochondria’ are not free-living

Many photosynthetic protists had secondary endosymbiosis





  • Algae ingested by other heterotrophic eukaryotes!
    • led to Euglenoids, Diatoms and Brown algae


  • Chloroplasts transferred to other protists
    • results in chloroplasts not from common ancestor!


  • How do we know this happened?
    • HINT: # of membranes around organelles = ____

Euglena: chloroplast with triple membrane


Eukaryotes have diverse reproduction


  • Haplonic life cycles: most life spent with one set of chromosomes (1N)
    • all cells are haploid (some multi-cellular algae, and fungi)
    • zygote only diploid cell → meiosis into daughter cells


  • Diplonic life cycles: most life with pairs of chromosomes (2N)
    • body cells (e.g., animals) are all diploid
    • sex cells (gametes) are haploid via meiosis → then fuse


  • Asexual life cycles: binary fission
    • nucleus divides, then cell divides into two separate organisms → mitosis
    • many-single celled protists can switch to asexual reproduction


  • There are more….
    • parasites require hosts

Life cycles in Eukaryotes: Alternation of Generations



  • More complex life cycles include an alternation of generations
    • some algae and plants
    • both generations must be multi-cellular


  • AOG = the alternation of multi-cellular haploid and diploid generations
    • diploid (2N) = sporophyte → makes spores
    • haploid (1N) = gametophyte → male/female → make gametes
    • fertilization of gametes makes new sporophyte


  • In some species the different generations look similar while in others they look different

Alternation of Generations: Basic Cycle


Protists matters: Ecology